UPS Systems Knowledgebase

Here you will find information about UPS. If you have any questions regarding existing or planned UPS systems, please do not hesitate to contact us.

A UPSUninterruptible (or Uninterrupted) Power-Supply protects end users primarily against power failures. It creates bridging time, e.g. to shut down servers in an orderly manner (thus preventing data loss) or e.g. until a generator has started up in the event of a power failure. It can create time buffers for mission-critical applications, increasing availability.

In addition, depending on the topology/model, UPSs protect against other power supply problems, up to and including permanent filtering of the power and thus ensuring consistent power quality, regardless of the state of the power grid.

Passive Standby / Off-Line

In normal mode, the UPS supplies the load and charges the battery directly from the mains. Only in the event of a mains failure or mains fluctuations does the UPS supply stable power from the battery. Inexpensive and usually sufficient for uncritical applications, office and home devices. Not suitable if the general power supply is of low quality.


In normal mode, the UPS is controlled by a microprocessor that monitors the quality of the power supply and reacts to changes. A compensation circuit ensures that the supply voltage is increased or decreased, compensating for mains fluctuations. The main advantage is that the compensation of overvoltage and undervoltage occurs without using the batteries. Used to protect IT applications against power failures, voltage dips, voltage spikes, overvoltage and undervoltage.

(Online) Double converter

Continuous protection of the power supply to critical end users against any problems that may arise. The output voltage is completely conditioned by double conversion by means of rectification and subsequent alternating direction and produces a power supply without any electrical disturbance. Double-conversion UPSs can be used for any type of loads, as they ensure trouble-free switching operations during the transition to battery operation. Online double conversion UPSs ensure a continuous quality of power supply, regardless of disturbances in the supply network.

1. Power grid failure

Lightning, destroyed lines, network overload, accidents and natural disasters, for example, lead to network failure.

2. Short-term undervoltage

For example, due to the switching on of large consumers, switching operations in the supply network, failure of network systems, lightning strike or power supply systems that are not able to cope with the requirements. In addition to pure failures, hardware can also be damaged.

3. Short-term overvoltage

Usually caused by lightning and can briefly raise the mains voltage to values of over 6,000 volts. A voltage spike almost always causes data loss or hardware damage.

4. Long-lasting undervoltage

For example, when the line voltage is intentionally lowered to reduce power during peak consumption periods or when the connected load exceeds the supply capacity.

5. Long-lasting overvoltage

Triggered by strong load reduction, disconnection of large consumers and other switching operations in the network. Hardware can be destroyed as a result.

6. Electrical interference signals with higher frequencies

Can be caused by electromagnetic interference (EMI) or radio frequency interference (RFI) from welding equipment, transmitters, printers, thunderstorms, etc.

7. Instability of the mains frequency

E.g. due to load changes on generators, especially smaller ones. Frequency deviations can cause faulty processes, data loss, system breakdowns and damage to equipment.

8. Peaks due to switching operations

Spikes usually lasting in the nanosecond range.

9. Harmonic distortion (harmonics) due to nonlinear load

Switching power supplies, stepper motors, copiers and fax machines, for example, are nonlinear consumer loads. They can cause communication errors, overheating and hardware damage.

As a rule, offline UPS cover points 1-3, line-interactive UPS points 1-5 and (online) double-conversion UPS points 1-9.

Double-conversion UPSs filter the power in any case and ensure consistent power quality throughout. They are therefore the best choice for critical applications.

The energy supply from a power plant initially always consists of three-phase alternating current. Single-phase AC can be drawn between one of the three phases and the neutral conductor or neutral conductor. Almost all PCs as well as small electronic devices use the single-phase power supply. Large air conditioners or other large consumers mostly use three-phase AC. What your network offers, how it is fused, which cable cross-sections and fuses are available and similar topics, or in case of doubt also what your consumers need, must be clarified with an electrician at least when planning larger UPS systems. This is also required for installation, except for plug-‘n-play UPSs.

UPSs come in a variety of form factors: small standby/offline UPSs are usually desktop units, often similar to a slightly thicker power strip or mini tower.

Lineinteractive UPSs are usually available as stand (tower) or rack-mountable models, often also as a combination solution of both form factors, wall-mounted devices are less common.

Online double conversion UPS are also available as rack or tower units, with larger or more powerful systems you quickly end up in cabinet size up to large systems that quickly bring along a large required footprint and a considerable weight (especially by the required batteries).

Determine the total power (in watts) of your loads to be protected. Important: the maximum current required, if any, is needed here, i.e. higher starting currents etc. must be taken into account, not just the modulating operation/average. Data sheets from the hardware manufacturers or measurements give a good indication here; the values from power supplies are not suitable, as these are usually (e.g. for most servers) significantly overdimensioned.

To allow for future expansion, we recommend installing a UPS with approximately 75% utilization. In addition, the capacity of batteries decreases over time, and here, too, appropriate oversizing helps to prevent problems.

Caution: The rated power of a UPS cannot be extended (or only in the case of larger scalable systems) and must therefore be planned well and future-proof.

When selecting the UPS, it is also necessary to take into account which connections the loads require. In the case of smaller UPS systems, the loads are usually connected directly to the UPS. In this case, it is necessary to clarify what type and quantity of individual connections are required (e.g. how many Schuko or Kaltgeräte connections). Often PDUs are used as a sub-distribution, here the appropriate connections are then also needed to match the PDU plug, but often a sub-distribution or a larger end user is installed hard-wired by the electrician, for this the UPS then requires an appropriate field/module for hard wiring.

In the event of a power failure, you will need sufficient bridging time or autonomy time to ensure proper shutdown of your systems or switchover to a backup generator.

In individual cases, a UPS should also be able to provide power for a longer time, e.g. to keep a POS terminal in operation; here, too, the required watts and duration are used for sizing.

You can add an additional external battery module (EBM) to many UPS models, if needed, to increase the UPS backup time (but not the total power).

… are an important issue, especially for larger UPS systems: make sure that the UPS can be brought to its final location. Will the UPS components fit through the doors? Are there stairs to climb? The UPS and battery cabinets can be heavy, so make sure the floor can support the weight of the equipment. UPSs use internal fans for cooling, batteries can outgas – the UPS should not be installed in a sealed container or in a small unventilated room. Make sure the UPS meets local building codes, this is where the building manager can provide the needed info.

A network card in the UPS allows access to the UPS from remote workstations or locations. It is also the basis for the use of software solutions and many services.

Software and services are a very complex topic in connection with UPSs. While the range in the area of software extends from power management to monitoring, alarming, etc., the range in the area of services extends from a possible necessary commissioning, ext. monitoring and maintenance up to repair. In short: state your requirements/wishes.

One of the central elements of any UPS are the batteries – they ensure that and how long your UPS can provide backup power. The most common type of battery for use in UPS systems is the (maintenance-free) valve regulated lead acid battery (VRLA). The standard service life of lead batteries is approx. 3-5 years (there are also LongLife variants with 8-10 or 10-12 years), but is strongly dependent on environmental conditions (especially temperature) and the number of discharge processes. Most UPSs monitor battery health and provide early warnings of the impending end of battery life. In many UPSs, the batteries are hot-swappable, i.e. they can be replaced during operation. Especially in the case of smaller systems, the exchange can be carried out by the user himself, without any special prior knowledge or tools. If necessary, batteries must always be replaced as a set, never individually.

Lithium-ion batteries are also being used more and more in UPSs. The higher purchase price is amortized in the medium term by a 2-3x longer service life, fewer or possibly no battery replacements required, and offers further advantages such as approx. 15% weight savings and approx. 3x faster charging than with VRLA batteries.

Further aspects…

… and questions such as redundancy, whether centralized or decentralized UPS, operation of a small UPS behind a large one or how UPS and generator work together, scalability or whatever else comes to mind, are best clarified in a personal discussion.

In general, we recommend that you always seek advice on the subject of UPS and do not spend a long time looking for the right solution – we will find it for you!